1. Field of the Invention
The present invention relates to a precoated skin material for an automobile interior part. In particular, the present invention relates to a precoated skin material for an automobile interior part comprising a skin material and a one-pack type thermally crosslinkable polymer composition comprising a specific thermoplastic polymer, a polyamine compound as a latent curing agent and a solvent.
2. Prior Art
As interior parts of automobiles, laminates comprising substrate layers and skin materials laminated on the substrate layers have been used to improve quality. Such a laminate is produced by a vacuum molding or press molding method in which an adhesive is applied to either one or both of the substrate layer and the skin material, and the molding and adhering are performed at the same time.
In such a molding method to adhere the skin material to the surface of the substrate layer by vacuum molding or press molding, a solvent-base adhesive is generally used, which comprises a polyesterpolyurethane containing a polyester as a polyol component dissolved in a solvent. However, this type of an adhesive has insufficient heat resistance required for the use in automobile interior applications, and a two-pack type adhesive containing a polyisocyanate as a curing agent is practically used. Such a two-pack type adhesive has some drawbacks such that it causes the environmental pollution since the adhesive is spray coated in a parts-molding line, and that the working time for mixing, coating and molding/adhering is restricted since two liquid components are reacted on mixing and cured.
One object of the present invention is to provide a one-pack type thermally crosslinkable polymer composition which can solve the above drawbacks of the conventional adhesives, and which is useful, for example, as an adhesive that is beforehand coated on a back surface of a skin material to provide a precoated skin material in the production of an interior part of an automobile.
Another object of the present invention is to provide a precoated skin material for an automobile interior part, which provides an automobile interior part comprising a substrate layer and a skin material adhered to the surface of the substrate layer, and which has initial heat resistant adhesion properties.
Accordingly, the present invention provides a precoated skin material for an automobile interior part comprising (a) a skin material for an automobile interior part and (b) a one-pack type thermally crosslinkable polymer composition comprising (i) a thermoplastic olefinic polymer having a carboxylic acid group or an acid anhydride group, (ii) a latent curing agent, (iii) a carbonyl compound as a solvent and (iv) a tackifier, which composition is coated on the back surface of said skin material, wherein said latent curing agent is at least one compound selected from the group consisting of solid polyamines having a melting point of 80 to 200xc2x0 C. which form hydrolyzable reaction products by a condensation reaction with said carbonyl compound used as the solvent, and hydrolyzable reaction products of diamines with carbonyl compounds.
The one-pack type adhesive used in the present invention can be stored at room temperature without the occurrence of a reaction, and crosslinked at a temperature of 60xc2x0 C. or higher to exert good adhesion strength with good heat resistance.
The thermoplastic polymers having a carboxylic acid group or an acid anhydride group may be olefinic polymers, butadiene polymers, ester polymers, carbonate polymers, urethane polymers, amide polymers, etc., all of which have a carboxylic acid group or an acid anhydride group. In particular, olefinic polymers having a carboxylic acid group or an acid anhydride group is preferable from the viewpoint of adhesion properties to polyolefins.
Typical examples of such thermoplastic polymers include polypropylene (PP), styrene-ethylene/butene-styrene copolymers (SEBS), ethylene-vinyl acetate copolymers (EVA), ethylene-acrylate copolymers (EEA), and the like, each of which is modified by the introduction of a dibasic unsaturated acid (e.g. maleic acid, fumaric acid, citraconic acid, mesaconic acid, etc.) or its anhydride. Such modified polymers are known and commercially available.
Hereinafter, thermoplastic polymers having a carboxylic acid group or an acid anhydride group will be referred to as xe2x80x9cCOOH-modified polymersxe2x80x9d.
Polyamine compounds used as latent curing agents are divided into the following two classes (I) and (II):
(I) Solid polyamine compounds having a melting point of 60xc2x0 C. or higher, preferably 80 to 200xc2x0 C., for example, aromatic polyamines such as 4,4xe2x80x2-diaminodiphenylmethane, 2,4xe2x80x2-diaminodiphenylmethane, 3,3xe2x80x2-diaminodiphenylmethane, 3,4xe2x80x2-diaminodiphenylmethane, 2,2xe2x80x2-diaminobiphenyl, 2,4xe2x80x2-diaminobiphenyl, 3,3xe2x80x2-diaminobiphenyl, 2,4-diaminophenol, 2,5-diaminophenol, o-phenylenediamine, m-phenylenediamine, 2,3-tolylenediamine, 2,4-tolylenediamine, 2,5-tolylenediamine, 2,6-tolylenediamine, 3,4-tolylenediamine, etc.; aliphatic polyamines such as 1,12-dodecanediamine, 1,10-decanediamine, 1,8-octanediamine, 1,14-tetradecanediamine, 1,16-hexadecanediamine, etc.; hydrazide base polyamine such as 1,3-bis(hydrazinocarboethyl)-5-isopropylhydantoin of the formula: 
(melting point: 121-123xc2x0 C.), the compound of the formula: NH2NHCOxe2x80x94(CH2)18xe2x80x94CONHNH2 (melting point: 174-181xc2x0 C.), the compound of the formula: NH2NHCOxe2x80x94(CH2)6xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)2xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)6xe2x80x94CONHNH2 (melting point: 147-155xc2x0 C.), the compound of the formula: NH2NHCOxe2x80x94(CH2)4xe2x80x94CONHNH2 (melting point: 177-183xc2x0 C.), the compound of the formula: NH2NHCOxe2x80x94(CH2)8xe2x80x94CONHNH2 (melting point: 186-188xc2x0 C.), the compound of the formula: NH2NHCOxe2x80x94(CH2)10xe2x80x94CONHNH2 (melting point: 189-191xc2x0 C.), isophthalic dihydrazide (melting point: 215-225xc2x0 C.); and the like. These polyamines may be used singly or in admixture of two or more.
An amount of the polyamine compound to be used is at least an equivalent amount to the carboxyl groups of the COOH-modified polymer. When the amount of the polyamine compound is less than the equivalent amount, the crosslinking of the polymer is insufficient, and the heat resistance of the cured material deteriorates. When the amount of the polyamine compound is too large, the curing agent is liberated, so that adherents may be insufficiently adhered. Accordingly, a preferred amount of the polyamine compound to be used is one to 10 times the equivalent amount.
(II) Hydrolyzable reaction products obtained by the reaction of diamines having two amino or imino groups in a molecule, and carbonyl compounds (aldehydes or ketones)
Examples of such diamines include aliphatic diamines (e.g. dimethylaminopropylamine, diethylaminopropylamine, monomethylaminopropylamine, methyliminobispropylamine, hexamethylenediamine, 1,10-diaminododecane, ethylenediamine, propylenediamine, butylenediamine, diethylenetriamine, di-xcex2-aminoethylsulfide, di-xcex2-aminoethyldisulfide, di-xcex2-aminoethylether, di-xcex3-amino-n-propylether, triglycoldiamine, N,N-dibutyltrimethylhexamethylenediamine, etc.); alicyclic diamines (e.g. 1,8-p-menhanediamine, isophoronediamine, diaminocyclohexane, 4,4xe2x80x2-methylenebis(cyclohexylamine), 1,3-bisaminomethylcyclohexane, 3-aminomethyl-3,3,5-trimethylcyclohexylamine, N,Nxe2x80x2-butylisophoronediamine, N-aminoethylpiperazine, 3-(3-aminopropyl)-3,2-dimethylpiperazine, etc.); aromatic or aromatic aliphatic diamines (e.g. xylylenediamine, diaminodiphenylether, phenylenediamine, triamionxylene, 4,4xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diaminodiphenylpropane, 4,4xe2x80x2-diaminodiphenylether, etc.); and the like. In particular, aliphatic diamines having 8 or more carbon atoms are preferred.
Furthermore, hydrolyzable reaction products can be prepared by reacting the solid polyamines (I) described above with carbonyl compounds.
The above carbonyl compound is generally represented by the formula:
R1xe2x80x94COxe2x80x94R2 
wherein R1 and R2 are the same or different and represent a hydrogen atom, a lower alkyl group having 1 to 8 carbon atom, preferably 1 to 6 carbon atoms (e.g. a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert.-butyl group, etc.), a phenyl group or a naphthyl group, or R1 and R2 together form a cyclic hydrocarbon group (e.g. a cyclohexyl group or a cyclopentyl group, etc.), provided that R1 and R2 are not hydrogen atoms or naphthyl groups at the same time.
Specific examples of the carbonyl compound include aliphatic aldehydes (e.g. acetaldehyde, propionaldehyde, n-butylaldehyde, isobutylaldehyde, diethylacetoaldehyde, etc.), aromatic aldehydes (e.g. benzaldehyde, etc.), cyclic ketones (e.g. cyclopentanone, trimethylcyclopentanone, cyclohexanone, trimethylcyclohexanone, etc.), aliphatic ketones (e.g. acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, diisopropyl ketone, dibutyl ketone, diisobutyl ketone, etc.); and the like.
The diamine and the carbonyl compound may be reacted under conventional conditions. For example, the diamine and an equivalent or excessive amount of the carbonyl compound in relation to the diamine are reacted in a suitable solvent (e.g. toluene, xylene, benzene, etc.), optionally in the presence of a water absorbent (e.g. molecular sieves, anhydrous magnesium sulfate, etc.) at room temperature or an elevated temperature while removing water.
Alternatively, the carbonyl compound may be added to the diamine subsequently. The reaction of the solid polyamine with the carbonyl compound thermally proceeds gradually during storage at room temperature resulting in the increase of the viscosity of the crosslinkable polymer composition. In such a case, when the carbonyl compound is used as a solvent, the increase of the viscosity of the composition is suppressed so that the shelf stability of the crosslinkable polymer composition is improved. Since the hydrolyzable reaction product is formed through the dehydration condensation reaction of the amino group and/or the imino group of the polyamine compound or the diamine compound with the carbonyl compound, the amino group and/or the imino group of the polyamine compound or the diamine compound do not cause the crosslinking reaction with the carboxyl group or the acid anhydride group of the crosslinkable polymer.
Here, a reaction product obtained using an aldehyde as a carbonyl compound is referred to as xe2x80x9caldiminexe2x80x9d, while one obtained using a ketone as a carbonyl compound is referred to as xe2x80x9cketiminexe2x80x9d.
Ketimines are usually less stable and more easily hydrolyzed than aldimines. That is, aldimines having a relatively low molecular weight have good shelf stability, while ketimines having a low molecular weight are unstable. Thus, solid polyamines and solid diamines having a relatively high molecular weight and good stability (low activity) are preferably used to prepare ketimines. More preferably, a reaction medium, which functions also as a carbonyl compound, is used, since the reaction is always in an equilibrium state.
An amount of the aldimine or the ketimine may be at least an equivalent amount to the carboxyl groups of the above COOH-modified polymer. When the amount of the aldimine or the ketimine is less than the equivalent amount, the degree of crosslinking is insufficient, and thus the cured carboxyl-modified polymer of the composition has low heat resistance. When the amount of the aldimine or the ketimine is too excessive, the adherents may be insufficiently adhered. Accordingly, a preferred amount of the polyamine to be used is one to 10 times the equivalent amount.
Examples of the carbonyl compound to be used as a solvent in the one-pack type thermally crosslinkable polymer composition of the present invention includes aldehydes and ketones. Specific examples of aldehyes are acetaldehyde, propionaldehyde, butylaldehyde, isobutylaldehyde, valeraldehyde, isovaleraldehyde, pivalaldehyde, capronaldehyde, heptaldehyde, caprylaldehyde, etc. Specific examples of ketones are acetone, methyl ethyl ketone, pentanone, hexanone, methyl isobutyl ketone, heptanone, diisobutyl ketone, acetonylacetone, mesityl oxide, phorone, isophorone, cyclohexanone, methylcyclohexanone, etc.
The carbonyl compound may be used in combination with other solvents such as aromatic solvents (e.g. toluene, xylene, benzene, etc.), cyclic alkanes (e.g. cyclohexane, etc.), halogenated hydrocarbons (e.g. 1,1,1-trichloroethane, methylene chloride, etc.), etc.
The carbonyl compound as a solvent may be used in an amount of at least 2% by weight provided that the thermoplastic polymer is not made insoluble, preferably from 5 to 15% by weight, based on the weight of the thermoplastic polymer. The carbonyl compound is usually used in an amount of 10 to 1,000 times equivalent to one equivalent of the latent curing agent.
The carbonyl compound to be used as the solvent in the composition of the present invention dehydration condensation reacts with the amino group and/or the imino group of the solid polyamine or the hydrolyzable reaction product to be used as the latent curing agent to form the hydrolyzable reaction product. As a result, the crosslinking reaction of the COOH-modified polymer having a carboxyl group or an acid anhydride group with the amino group and/or the imino group of the solid polyamine or the hydrolyzable reaction product is suppressed, and thus the shelf stability of the composition is improved. Furthermore, the storage stability of the precoated skin material carrying the beforehand coated adhesive is also improved. In addition, the adhesion properties, in particular, heat resistant adhesion properties is improved when the precoated skin material is vacuum adhered by heating to the substrate layer.
When the amount of the carbonyl compound is less than 2% by weight, the viscosity of the composition increases. When the amount of the carbonyl compound exceeds 15% by weight, the solubility of the COOH-modified polymer may decrease.
The one-pack type thermally crosslinkable polymer composition of the present invention preferably comprises the COOH-modified polymer, the solid polyamine (I) or the aldimine or ketimine (II), which are dispersed in the above specific ratio in the carbonyl compound as the suitable organic solvent. If desired, the one-pack type thermally crosslinkable polymer composition of the present invention may optionally contain a conventional thermoplastic resin (e.g. acrylic resin, vinyl resin, polyamide resin, polyester resin, polyolefin, polyurethane, SEBS, etc.), tackifiers, polyolefin-base tackifiers, dyes, pigments, etc.
The one-pack type thermally crosslinkable polymer composition of the present invention having the above composition can be used as an adhesive, a coating material, an adhesive sheet, a film or sheet-form adhesive, a paint, and the like. In particular, the one-pack type thermally crosslinkable polymer composition of the present invention is useful as an adhesive which is used in the production of laminates for automobile interior parts, which comprise a substrate layer (e.g. ABS boards, polyphenylene oxide (NORYL(copyright)) boards, ASG boards, polycarbonate boards, polypropylene boards, wood composite boards, steel plates, etc.) and skin materials (e.g. polyvinyl chloride foams, polyolefin foams such as polyethylene foams, polypropylene foams, etc.).
One example of the skin material is described by Makoto Ohyama et al, xe2x80x9cSolvent-Free Adhesive Technology for Instrument Crash Pad Vacuum Formingxe2x80x9d, International Congress and Exposition, Detroit, Mich., Feb. 27-Mar. 2, 1995 (SAE International). This literature describes a laminate skin material having a polyvinyl chloride sheet and a polypropylene foam. Furthermore, the skin material may be a polymer sheet or a laminate of a polymer sheet and a polymer foam laminated on the back surface of the polymer sheet. The polymer sheet is preferably a polyolefin sheet, in particular, a polypropylene sheet.
The thermally crosslinkable polymer of the present invention is usually applied to the back surface of the skin material, that is, the surface which faces the substrate layer.
The production steps of such laminates will be explained in detail.
i) Firstly, the polymer composition of the present invention is precoated in a thickness of 5 to 500 xcexcm uniformly on the back surface of a skin material, and dried at a temperature of room temperature to 100xc2x0 C., for example, 50 to 100xc2x0 C. for several seconds to several minutes. The dry thickness of the composition is from 10 to 300 xcexcm.
Alternatively, the polymer composition of the present invention may be discontinuously coated on the back surface of a skin material. For example, the polymer composition may be coated in a linear (or bead) form or a dot form. In the case of discontinuous coating, the amount of the polymer composition can be reduced to about half to two thirds of the amount in the case of the overall area coating. The polymer composition may be discontinuously applied with a multi-nozzle, or transferred with a roll or a doctor knife coater
By the above application methods, an adhesive layer having no blocking properties is formed on the skin material. The precoated skin material may be supplied to a following molding process as such, or it may be stored for a certain time, for example, several months at a temperature of room temperature to 50xc2x0 C. and then supplied to the molding process. Even when the precoated skin material is stored for a long time, it can exert a sufficient adhesion force.
When a latent curing agent in the adhesive layer of the precoated skin material is the aldimine or the ketimine, it tends to be easily hydrolyzed with moisture (or water) in an air to form a free amine and to cause the hydrolysis. Thus, the precoated skin material should be stored in a dry state in a sealed container during the storage or in the period prior to molding in a subsequent step.
ii) Then, the precoated skin material produced in the step i) is laminated on a substrate heated at a specific temperature (usually around 60xc2x0 C.) while optionally heating the skin material at a certain temperature (usually from 100 to 180xc2x0 C.), if desired, and heat pressed under a pressure of 0.1 kg/cm2 or more for at least 10 seconds to effect the molding and adhering at the same time. Thus, a laminate having good heat resistant adhesion properties. In addition, such a molding process can prevent environmental pollution caused by the evaporation of solvents.
Such laminates can be used as automobile interior parts such as inside trims (e.g. door trims, front pillars, deck side trims, center pillars, etc.), instrument panels, molded ceilings, console boxes, and the like.
In the above, the polymer composition of the present invention is explained in connection with its application as a precoating adhesive of skin materials, that is, an adhesive which is beforehand coated on skin materials, although it can be advantageously used as a thermally crosslinkable adhesive film, sheet or tape having a thickness of 50 to 500 xcexcm by forming, that is, coating and drying, the composition on a suitable support such as a release paper. In such a case, the properties of the film may be adjusted by the addition of the above-described thermoplastic resins.